Relief images can be provided and used in various articles for many different purposes. For example, the electronics, display, and energy industries rely on the formation of coatings and patterns of conductive materials to form circuits on organic and inorganic substrates. Such coatings and patterns are often provided using relief imaging methods and relief image forming elements. There is also need for means to provide fine wiring in various articles.
Microelectronic devices have been prepared by photolithographic processes to form necessary patterns. Photolithography, however, if a complex, multi-step process that is too costly for the printing of plastic electronics.
Contact printing is a flexible, non-lithographic method for forming patterned materials. Contact printing potentially provides a significant advance over conventional photolithographic techniques since contact printing can form relatively high resolution patterns on plastic electronics for electronic parts assembly. Microcontact printing can be characterized as a high resolution technique that enables patterns of micrometer dimensions to be imparted onto a substrate surface. Contact printing is a possible replacement to photolithography in the fabrication of microelectronic devices, such as radio frequency tags (RFID), sensors, and memory and back panel displays. The capability of microcontact printing to transfer a self-assembled monolayer (SAM) forming molecular species to a substrate has also found application in patterned electroless deposition of metals. SAM printing is capable of creating high resolution patterns, but is generally limited to forming metal patterns of gold or silver for example using thiol chemistry. Although there are variations, in SAM printing a positive relief pattern provided on an element having a relief image is inked onto a substrate.
Flexography is a method of printing that is commonly used for high-volume printing runs. It is usually employed for printing on a variety of soft or easily deformed materials including but not limited to, paper, paperboard stock, corrugated board, polymeric films, fabrics, metal foils, glass, glass-coated materials, flexible glass materials, and laminates of multiple materials. Coarse surfaces and stretchable polymeric films are economically printed using flexography.
Flexographic printing members are sometimes known as “relief” printing members (for example, relief-containing printing plates, printing sleeves, or printing cylinders) and are provided with raised relief images onto which ink is applied for application to a printable material. While the raised relief images are inked, the relief “floor” should remain free of ink. The flexographic printing precursors are generally supplied with one or more imageable layers that can be disposed over a backing layer or substrate. Flexographic printing also can be carried out using a flexographic printing cylinder or seamless sleeve having the desired relief image.
Flexographic printing members can be provided from flexographic printing precursors that can be imaged flat or “in-the-round” (ITR) using either a photomask or laser-ablatable mask (LAM) over a photosensitive composition (layer), or they can be imaged by direct laser engraving (DLE) of a laser-engraveable composition (layer) that is not necessarily photosensitive.
Gravure or intaglio printing members are also relief printing members in which the image to be printed comprises depressions or recesses on the surface of the printing member, where the printing area is localized to the areas of depression that define the pattern or image. The process for using gravure or intaglio printing members is the reverse of flexographic relief printing wherein an image is raised above the floor of the flexographic printing member and the printing area is localized at the contact area of the top surface protrusions.
Laser ablation or laser engraving can be used effectively with an appropriate laser-engraveable precursor to form images for either of the above-mentioned printing processes.
Flexographic printing precursors having laser-ablatable layers are described for example in U.S. Pat. No. 5,719,009 (Fan) where precursors include a laser-ablatable mask layer over one or more photosensitive layers. This publication teaches the use of a developer to remove non-reacted material from the photosensitive layer, the barrier layer, and non-ablated portions of the mask layer.
There has been a desire in the industry for a way to prepare flexographic printing members without the use of curable photosensitive layers that require liquid processing to remove non-imaged composition and mask layers and that generate significant amount of liquid waste. Direct laser engraving of precursors to produce relief printing plates and stamps is known, but the need for relief image depths greater than 500 μm creates a considerable challenge when imaging speed is also an important commercial requirement. In contrast to laser ablation of mask layers that require low to moderate energy lasers and fluence, direct engraving of a relief-forming layer requires much higher energy and fluence. A direct laser-engraveable layer must also exhibit appropriate physical and chemical properties to achieve “clean” and rapid laser engraving (high sensitivity) so that the resulting printed images have excellent resolution and durability.
A number of elastomeric systems have been described for construction of laser-engraveable flexographic printing precursors using various elastomeric rubber compositions in the laser-engraveable layers as described for example, in U.S. Pat. No. 6,223,655 (Shanbaum et al.), U.S. Pat. No. 4,934,267 (Hashimoto), and U.S. Pat. No. 5,798,202 (Cushner et al.). Although many polymers are suggested for this use in the literature, only extremely flexible elastomers have been used commercially because flexographic layers that are many millimeters thick must be designed to be bent around a printing cylinder and secured with temporary bonding tape and both must be removable after printing.
Thermoplastic elastomeric composition comprising partially crosslinked blends of ethylene copolymers and vinyl or vinylidene halide polymers are described in U.S. Pat. No. 4,613,533 (Loomis et al.), U.S. Pat. No. 4,739,012 (Hagman), and U.S. Pat. No. 7,282,242 (Abell, III, et al.).
The vulcanization of rubbers is a time-consuming, labor-intensive, multi-step process with significant batch-to-batch variations. Inconsistencies in curing and components lead to considerable waste in manufacturing, which brings increased costs and environmental problems. In addition, vulcanization requires the use of various sulfur or peroxide vulcanization agents, but such reactive compounds can produce objectionable odors. In general, the vulcanized compositions known in the art are non-processable, non-reshapeable, and non-recyclable.
Polyvinylchloride is a thermoplastic polymer but it has a glass transition temperature that is above ambient temperature and is therefore a rigid thermoplastic polymer and thus does not offer the flexibility, elongation, and compression recovery properties required for flexographic printing plates or other printing plates that need to be wrapped around a print cylinder. Polychloroprene (or neoprene) offers excellent compressibility and elongation, but it is a vulcanized (or crosslinked) rubber and therefore it is a thermoset polymer, which cannot be readily re-melted and reprocessed into another printing plate precursor.
There is a need to avoid the problems associated with conventional vulcanizing processes and to provide direct laser-engraveable compositions that are useful for providing relief images and that can be prepared with reduced material waste and even recycled for re-use.